Whose uncool trousers split to reveal what's underneath? (4,4,4,7)

I believe the answer is:

show ones true colours

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'whose uncool trousers split to reveal what's underneath?' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'whose uncool trousers split' is the wordplay.
'split' indicates anagramming the letters (letters split up and reassembled).
'whose'+'uncool'+'trousers'='whoseuncooltrousers'
'whoseuncooltrousers' with letters rearranged gives 'SHOW ONES TRUE COLOURS'.

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